Depolymerization of Lignosulfonate Catalyzed by Different Solid Base Oxides to Prepare Phenolic Compounds

Lignin is the most abundant aromatic renewable polymer in nature. However, its very stable structure limits its widespread application. To achieve high-value utilization of lignin, this study used solid base oxides to depolymerize calcium lignosulfonate (CLS) for the synthesis of phenolic compounds. The catalyst precursors were prepared by hydrothermal synthesis, and the corresponding mesoporous metal oxides NiO, MgCoOx, and NiMgCoOx were obtained after calcination. MgCoOx and NiMgCoOx had similar but stronger basicity compared to NiO. While all oxides promoted the depolymerization of CLS, NiMgCoOx was identified as the best catalyst, achieving a maximum liquid product yield of 74.3 wt.% and a selectivity of phenolic compounds of 74.52% in the liquid product. In addition, NiMgCoOx showed satisfactory structural and catalytic stability. The experimental results indicated that solid base oxides can capture the active hydrogen in CLS, causing the hydrolysis reaction of ether bonds, and the resulting products continuously depolymerize or polymerize; Co present in the catalyst promotes the adsorption of hydrogen by Ni, while NiO in NiMgCoOx facilitates the adsorption of both reactants and hydrogen. The combination of Ni and Co improves hydrogenation performance.